Battery-powered devices (e.g., consumer electronic devices, electric and hybrid automobiles, etc.) are charged from a power source (e.g., AC power outlet) through a charging device. The charging device couples the battery to the power source through an adaptor. The cord extending between the power source and the battery-powered device can take up space. In situations where multiple devices require charging, each with their own charger and cord, the charging area can become cramped and inconvenient.
Approaches are being developed that use over-the-air or wireless power transmission between a transmitter and a receiver coupled to the electronic device. Wireless power transmission using inductive coils is one method considered as an un-tethered method for transferring power wirelessly through a coupled magnetic field. In wireless power transmission, power is transferred by modulating a magnetic field with a transmit coil. On the receiver side, a receiver coil may couple to the magnetic field modulated by the transmit coil, thus, wirelessly receiving power from the transmit coil. The efficiency at which power can be transferred wirelessly depends on the design and size of the transmit and the receive coils as well as the geometry between the transmit and the receive coils.
Because higher power transfer efficiency can result in reduced power consumption and reduced recharging time, it would be advantageous to use coil designs that improve power transfer efficiency. Accordingly, it would be advantageous to use higher efficiency coil designs to support wireless power transmission.